The invention relates to a system for reproducing information signals, recorded on a magnetic tape in parallel adjacent tracks which extend obliquely relative to the longitudinal direction of said tape, in different modes of operation with different predetermined speeds of the magnetic tape, which modes can be switched on by actuation of a mode selection device, which system comprises a tape-drive device which is switchable to drive the magnetic tape at different speeds, at least one magnetic head which is rotatable by means of a head-drive device for consecutively scanning the tracks, and a tracking servo system for guiding said head along the tracks, which servo system, in order to position the magnetic head in a direction transverse to the tracks, comprises an electromechanical positioning device which can be driven by a drive signal, which comprises a tracking signal generated by a control circuit of the tracking servo system, and a sawtooth-shaped control signal whose waveform is adapted to the instantaneous speed of the magnetic tape, and a variable-waveform sawtooth generator for generating the sawtooth-shaped control signal, there being provided a switching device which is responsive to the actuation of the mode-selection device to produce at least one switching signal for switching over the tape-drive device and the sawtooth generator when the mode of operation is changed, which switching device switches over the tape-drive device as regards the speed of the magnetic tape and the sawtooth generator as regards the signal waveform of the control signal in a predetermined switching process and in conformity with each other.
A system of the type specified in the foregoing is known, for example, from the video tape recorders which are commercially available under the type designations VR 2024 and VR 2220 for the recording and/or reproduction of television signals. By means of these video recorders, television signals can be recorded on the magnetic tape in parallel contiguous tracks which extend obliquely to the longitudinal direction of said tape at a so-called normal speed of the tape by means of two magnetic heads which are arranged diametrically opposite one another on a rotatable magnetic-head unit. Normal reproduction of television signals thus recorded is effected at the same normal speed with which they had been recorded. In order to obtain special motion effects, such as slow-motion or fast-motion effects, and also to enable a so-called search mode for the rapid location of specific pictures, these recorders can also reproduce the television signals in modes which differ from normal reproduction, the speed of the magnetic tape differing from the normal speed both as regards the magnitude and the sign, which defines the direction of movement of the magnetic tape, the tracking servo system ensuring that despite the changed scanning conditions, the magnetic heads accurately follow the tracks recorded on the magnetic tape, so that also in these reproduction modes, a correct and undisturbed reproduction of the television signals is guaranteed. It is obvious that these video recorders may also be switched from one reproduction mode to another, for example, once the desired picture has been found after a search mode, a normal reproduction mode may be selected.
In the system used in the two known video recorders for the reproduction of television signals, switching between two reproduction modes with different speeds of the magnetic tape, is effected abruptly when the user actuates a corresponding mode switch of a mode-selection device comprising a plurality of mode switches. When such a mode switch is actuated, both the tape drive device and the sawtooth generator of the tracking servo system must be set immediately to the operating values corresponding to the desired mode in a single-step switching operation. However, since both the tape-drive device and the electromechanical positioning devices of the tracking servo system for the two diametrically arranged magnetic heads, which positioning devices are driven by the sawtooth-shaped control signal from the sawtooth generator, are not capable of performing comparatively large abrupt jump-like of movement changes because their dynamic properties and, moreover, the dynamic properties of the tape-drive device and the positioning devices of the tracking servo system differ completely from each other, the coordinated, mutually synchronous operation of the tape-drive device and the tracking servo system, by means of which the magnetic heads follow the tracks recorded on the magnetic tape driven by the tape-drive device, is lost temporarily when the mode of operation is changed. In the case of such a change of mode, this results in the scanning of the television signals stored in the tracks, being disturbed, which in turn gives rise to annoying disturbances in the reproduction of the television signals on the screen of a television receiver.